After uptake by competent S. sanguis cells, and prior to genetic integration into the recipient chromosome, donor DNA exists in a single-stranded (s.s.) form complexed with recipient protein. Initially a s.s. donor DNA-protein (pre-synaptic) complex forms external to the cell membrane. Subsequently, a similar (synaptic) complex is found internally and non-covalently associated with the recipient chromosome just before integration. In order to discover the functions of these s.s. donor DNA-protein complexes, we shall first seek to isolate and characterize the protein obtained from presynaptic complexes. We then intend to purify this protein in relatively high yield. With specific antibodies prepared against the purified protein, we will be able to determine its cellular location prior to uptake of transforming DNA as well as its identity (or non-identity) with the protein in synaptic complexes. Finally, the purified protein will also enable us to attempt construction of presynaptic complexes in vitro, to determine the conditions for their formation and the efficacy with which they synapse in vitro with double-stranded DNA of varying degrees of superhelicity.